1. Field of the Invention
The present invention relates to a method of grinding a half toroidal CVT disk used as a continuously variable transmission in an automobile.
2. Description of the Related Art
A half toroidal CVT disk includes a disk-shaped disk main body 1; and, as shown in FIG. 5, the disk main body 1 has an inner surface portion 2 consisting of a through hole formed in the central portion thereof, an outer surface portion 3, and a toroidal surface 4 formed on one surface of the disk main body 1. On one end side of the inner surface portion 2, there is formed an inner surface involute spline portion 5; and, on the other end side thereof, there is formed an inside diameter surface 6. And, the toroidal surface 4, inner surface involute spline portion 5 and inside diameter surface 6, except for the outer surface portion 3, must be respectively ground so as to have concentricity accuracy of a given value or higher.
For this reason, conventionally, for example, as disclosed in JP-A-2000-271844, in a state where the outer surface portion 3 is centered with the inner surface involute spline portion 5 as the standard thereof and is chucked in the thus centered state, the outer surface portion 3 is ground; and, with the thus ground outer surface portion 3 as the standard thereof, the toroidal surface 4 and inner surface portion 2 are respectively ground in separate steps.
Also, as a compound grinding machine, conventionally, there is known a compound grinding machine which, as disclosed in JP-A-10-235545, comprises a plurality of spindle devices each including a work chuck for chucking a work, while these spindle devices are carried on a swing table which is capable of indexingly swinging in such a manner to be able to correspond to a plurality of operation positions. At these operation positions, there are disposed two or more kinds of grinding devices and, using the grinding devices, the works chucked by the work chucks are respectively ground to thereby shorten the grinding time.
In case where the toroidal surface and inner surface portion of the half toroidal CVT disk are ground in separate steps, it is necessary to grind the outer surface portion as the common standard surface for securing the concentricity of these grinding surfaces. However, to grind the outer surface portion is not necessary for the function of the half toroidal CVT disk and thus the step of grinding the outer surface portion provides a great factor in the increased cost of the half toroidal CVT disk.
Also, there must be secured concentricity between the inner surface involute spline portion to be worked prior to the heat treatment of the half toroidal CVT disk and the toroidal surface and inner surface portion to be ground.
Further, in case where the outer surface, inner surface portion and toroidal surface are ground sequentially in separate steps, the half toroidal CVT disk not only must be mounted onto and removed from the grinding machines but also must be delivered between the grinding machines in these respective grinding steps, which makes it troublesome to grind the half toroidal CVT disk and thus provides an important factor in the increased cost thereof.
Still further, in the case of the toroidal surface grinding operation, there is a limit on the diameter of a grinding wheel and the direction of the rotary shaft of the grinding wheel must be set at an angle of 58°-65° (±15°) with respect to the direction of the rotary shaft of the work.